Sign



June 18, L929. F. K. RICHTMYER A 1.717.938

SIGN

. Filed Aug. 5, 192'? INVENTOR- ATTORNEY Patented June 18, 1929.

ifilit,

UNITED STATES PATENT OFFICE.

ELO'QD K. RICILTMYER, OF ITHACA, NEW YORK, ASSIGNOR, BY MESNE ASSIGNMENTS,

TO RAY-SIGNS CORPORATION, A. CORPORATION OF DELAWARE.

SIGN.

Application filed August 3, 1927. Serial No. 210,446.

My invention constitutes an improvement in signs or other public notices, the charac-' ters in which are formed by the assembly in proper arrangement of a plurality of optical reflecting units, which become luminous and have the appearance ofbeing self-' illuminated as a result of the reflection of light directed upon them, somewhat after the property of animals eyes in the dark. These :0 optical units are composed each of an objective lens of glass or equivalent material and a reflector suitably associated with the ample, the unit be employed in a roadside sign, which at night-is intended to be i1- luminated by the headlights of passing vehicles, it is necessary that the reflected light be sufliciently diverging to strike the eyes of the occupantsof the car,which are usually on a level considerably above that of the headlights. Also it is necessary that the component units of the sign be equally luminous irrespective of the precise'path of the vehicle, or, in other words, the precise angleat which the light is thrown upon the vsign by the headlights. The units should 35 also present a uniform appearance, i. e. should be of uniform brightness. This means exact reproduction of dimensions from one unit to another, appearance being. very sensitive to change of dimensions.

The most satisfactory reflecting device heretofore devised and employed for this purpose is one in which the lens is composed of a cylindrical glass body having a I convex spherical front end and a lano-rear 4 end, together with a concave re ector disposed behind the lens in axial alignment therewith. The dimensions and relative disposition of the parts are comparatively crit- -ical. For example, it has been found that,

substantially 1.5, the best results are obtained if the length of the glass body be substantially twice the radius of curvature of the spherical front end and the radius through a comparatively wide range of" for glass having an index of refraction of of curvature of the concave reflector be substantially two-thirds the length of the body, the reflector being disposed-immediately behind the plano end, and having its center coincident with that of the spherical end of the lens. Ithas been the practice with this type of unitto make the reflector of polished metal with a cylindrical sleeve portion fitting over the rear end of the cylindrical glass body, the unit ordinarily being set with its rear end in. cement so as properly to protect the inner surface of the reflector from dust and moisture.

Modifications of this general form of refleeting unit have been proposed including units .in which the objective and the mirror are made in one piece from glass the limiting active surfaces of which are portions ofspheres having a common center and having their active surfaces opposed to one another. As far as I am aware, however, none of these proposed modified forms has proven commercially successful and, so far as they have been tested, they have proven inferior in-their optical performance to the one above referred to, in which the mirror is a sep arate element and the lens is plano-convex.. The light utilization, for example, I of the unitary structure mentioned above decreases with increasing angle of incidence.

However, there are definite advantages structurally in having the lens and reflector unitary. Since the relative dis osition of the, surfaces is critical, a unit aving two surfaces is superior from a manufacturing and assembling stand oint to one having three surfaces, 'as wit the latter there is always a possibility of maladjustment in assembling which is eliminated with the former. Furthermore, the unita-r structure can i be made more simple and c eaply.

The unit constituting my invention-is com posed of a cylindrical lass' body having the front end of lenticuTar power to serve as the objective and the rear end made convex and silvered and constituting the min ror, the len th of the body and, the radii of the ends being such for a given index of refraction of the .glass that oblique as well as axially parallel incident rays will within a wide angular range be returned in toto ,or substantially so as a diverging cone of light the axis of which is substantially parallel to the direction of the incident rays. The rekind, as a result of which the central ray of the cylindrical bundle of rays incident upon the front or objective surface of the unit, remains after reflection the central axial ray of the reflected cone of rays, not only when the axis of. the incident bundle is parallel to the axis of the unit but when these two axes make comparatively large anglesas much as 30with each other.

So far as I am aware, no unitary device has. yet been disclosed which accomplishes thisf "bundle of light, i. e., a bundle of light whose result. v The innovat1on consists in discarding the concentric princi le usually employedin devices of this kin and in substituting there for a dispositionof the active surfaces, s herical, parabolic or otherwise, so that the a ve mentioned central ray of the incident 1 bundle after refraction at the front (0b jectivei surface meets the rear reflecting surface at substantially normal incidence, as a result of which this ray is reflected, at this rear surface, so as to retrace its path back through the system. At the same timethe extra axial rays of. the incident bundle are.-

more or less symmetrically reflected so as to emerge symmetrically on the o posite side of the axial ray. I have found by giving to the rear surface a ra ius of curvature about twice that of the front surface, (more or less depending on the index of refraction of the glass used, as is indi-' cated by the illustrative data below) and by I placing the center of curvature of the rear surface approximately midway between the center of curvature of the front surface and the vertex of that surface. The net result ofthis innovation is to increase the effective a erture of the objective surface for an o liquel incident bundle' of rays over and above t e corresponding aperture of those devices in which the concentric adjustment of the two spherical surfaces is employed.

In the drawings, I have shown diagrammatically theoptical rformance of a unit embodying my invention:

Fig. 1 1s a diagram showing the lens in cross section and showing the action of the Fig. 3 is a section of a that with, spherical surfaces this can be accom lished' Fig. 4 is an elevation of a-modified form of lens embodying my invention.

The illustrated unit is a'cylindrical glass body with a spherical front or objective end F with its center of curvature-at 0,, and with a spherical rear end R which is silvered and which has its center of curvature at 0,.

The index of refraction of the illustrated unit is chosen at 1.52. The center of cu-rvature 0 of the rear face R is substantially midway between the center of curvature 0 of the front face F and the axial center or vertex of that face, and the radius of curvature of the; rear face is substantially 2.2 times the radius of curvature of the objective or front face, the length of the unit being therefore 2.7 times the front radius.

The dia ram of Figure" 1 illustrates the 4 function '0 the unit upon an axially parallel direction of incidence is parallel to the axis of the unit. 'The rays 73, r r r, are refracted on entering the glass medium and converge to within a small area of the mirror R by which the are reflected along the paths indicated an emerging from the glass and are returned as the rays 5,, 8 s 8,, respectively;- The rays of the reflected hundleam first converging and then diverging due to the fact that they are notbrought to a sharp focus on the'mir ror, .or, in other words, due to thc spherical aberration of the system. desired. spread is obtained, the proportions and the dimcnsionsbeing soselected that the angle ofdeviation of the emergent rays with p are again refracted on In this way the the direction of incidence is just enough for allel incident rays.

In Figure 2 is shown a unit of the same dimensions and same kind of glass as Figure 1, and illustrating diagrammatically the action of the unit upon an oblique incident bundle of rays. chosen for this illustration is 225. The incident rays 1' r 1 r r 9 are returned as rays 8,, s s 8,, s 8 the reflected light being a cone with its axis substantially parallel to the direction of incidence. The cone is convergent to a degree just enough to give the desired spread to the light at the distance at which the signs are usually observed.

important feature of the operation of my unit is the fact that the central in cident ray 7', remains the central ray 8, of the light returned, whatever the angle of incidence. For a given index of refraction of the glass, the center 0 is so located that for angles of incidence not exceeding a per missible maximum either side of axial parallelism) the central incident ray is so refracted as to pass through the center 0 and hence, entering along a line of radius of the rear face, it is substantially The angle of incidence returned along the same path. It'will results wherea wi understood that the exact position of the center of curvature and length of radius of the rear face vary somewhat according to the index of refraction of the glass and the .use to which the unit is to be put and at best are but approximations, but I have found the followin dimensions to give "00d 5e range of angles 0 incidence and a'small divergence of the refiected cone are desired:

Index of Front Rear refraction radius radius Length 1. 50 R 2. 2R 2. 7R 1. R 1. 98R 2 48R 1. R 1. 78R 2. 28R

It will be noted that in the above table I have assumed that 0 remains exactly half Way between 0 and the front vertex. The central incident ray will always be refracted so as to pass substantially through the center 0 and therefore strike thefrefiecting surface R at normal incidence'.f' The radius of the rear surface is so chosen that as illustrated in Figure 2, the rays other than the central ray are symmetrically reversedm ihe ray T for example, emerges as ray .9 which two rays are symmetrical with respect to the central ray 1' Similarly the ray r which strikes the front face at normal incidence and travels along a radius of the center 0 is displaced sidewise substantiallyan equal distance on the other side of the ra 7;, due toits angle of incidence on the relihctor R. The cross sectional area of the reflected bundle of light is substantially that of the incident bundle, and this effective aperture of the unit is substantially unaffected by changing the an is of incidence.

This desirable unction'of my unit in lar e part results from the fact that the center 2 is in advance of. the center 0 The precise disposition of the center 0 and length of the radius of curvature of the mirror depend somewhat upon the use.

In Fig. 3, Lhave shown two of my units as they will be mounted in a sign. Each lens Z is mounted with its rear silvered end in a metallic cap C in which it is cemented. The silvered end is thereby hermetically sealed against dirt and moisture. The'caps limited to this preferably have flat on s normal to the axis of the lenses, the sleeve portions of theica s assuring proper relative disposition of t e lenses in the caps. The rear ends of the units maybe imbedded in cement, Jasindi- I that for a given index or refraction of the caged in the figure.

' t is obvious that my invention -is not ing theunits in the sign. It may also be commented that the rear end if the unit .tially twice that of the front precise method for pmtccting the silvered ends of the units or for mountgreater range qf aspect, as.

Various" other "modi made in the illustrated 1. 'An optical unit of the reflecting type v comprising a glass body having its ends convcxly spherical and having its rear'end refiective, the center of curvature of the rear face being so positioned for the particular index of refraction of the glass and the radius of the rear face being such that the central or axial ray of an oblique bundle of incident rays of light will pass substantially through said center and the extra-axial rays of theincident bundle will be substantially symmetrically reflected so as to emerge symmetrically on the side ofthe axial ray opposite to that of their incidence.

2. An optical unit of the reflectin type comprising a glass body having its ends convexly spherical and having its rear end refiective, the center of curvature of the rear face being so positioned for the particular index of refraction of the glass and the radius of the rear face being such that the central or axial ray of an oblique bundle of incident rays of light will pass substantially through said center and the extra-axial ra s of the incident bundle will be substantial y symmetrically reflected as a diverging cone of 1i ht the axis of which is substantially paraflel to the direction of incidence.

3. An optical unitof the reflectin comprising a glass body having its end vexly i ieotive the center of curvature of the rear ace of the front face and the axial center of front face, and the radius of curvature of the rear face being substantially twice that of the front face.

4-. An optical unit of the reflecting type comprising a glass body having its en s convexly spherical and-having its rear end reflective, the center of'curvature of the rear face being substantially midway between the center of curvature of the front face and of curvature of the rear face being substanface. 5. An optical unit of the reflecting type comprising a lens and a concave reflector at the rear end of the lens, the center of curvabeing between the center-of curvature the axial center of the front face, and the radius Y ture of the reflector being so located in ad vance of the center ofifeburvature of the lens radius of the reflector exceeding t at of the 4 p Y amas front face of the lens and proportioned thereto so that the extra axial rays of the incident bundle will be substantially symmetrically reflected so as to emerge symmetrically on the side of the axial ray opposite to that of their incidence.

'6. An optical unit of the reflecting type -comprising a lens and a concave reflector at the rear end of the lens, the center of curvature of the reflector'being so located for a given index of refraction of the material ofthe lens that the central ray, of an incident the reflector being substantially twicelthat of the front face of the lensg' I 7. 'An optical unit of. the reflecting type comprising a lens and a concave reflector 2e behind the lens disposed with as vertex substantially at the focal point of albundle of rays axially incident upon the lens and having its center of curvature on the axis of the system substantially at the point Wherefthe axis is intersected by the line of incidence upon the reflector of the central ray of a bundle of rays obliquely incident upon theobjective face of the lens.

In witness whereof, I hereunto subscribe #0 my signature.

' FLOYD K. RICHTMYER. 

